Polarized light source device and back light module for liquid crystal display

ABSTRACT

A polarized light source device comprises a light source, a reflector, a transparent substrate, an antireflection layer, and a plurality of metal grid wires. The reflector surrounds the light source for reflecting the light, and has an opening for emitting the light. The transparent substrate is disposed at the opening. The antireflection layer is disposed on the transparent substrate. The metal grid wires are disposed on the antireflection layer for transmitting the light with a predetermined polarization therethrough.

CROSS REFERENCE TO RELATED APPLICATION

The present application is a divisional continuation of U.S. patentapplication Ser. No. 10/446,663, filed May 29, 2003, now U.S. Pat. No.7,264,390 which claims priority from Taiwan Patent Application SerialNumber 091125380, filed Oct. 23, 2002 and Taiwan Patent ApplicationSerial Number 091136762, filed Dec. 16, 2002, the disclosures of whichis hereby incorporated by reference herein in their entirety.

The present application is also related to U.S. patent application Ser.No. 11/461,650, filed Aug. 2, 2006.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention generally relates to a polarized light sourcedevice, and more particularly, to a back light module for a liquidcrystal display (LCD) which provides polarized light with hightransmittance.

2. Description of the Related Art

Referring to FIG. 1, it depicts the structure of a conventional liquidcrystal display. Generally, the liquid crystal display device includes aliquid crystal display panel 10 which has two substrates and a liquidcrystal material sealed therebetween, a back light unit 20 disposedunder the liquid crystal display panel 10, and cases 11 and 12.

The back light unit 20 is utilized to distribute the light from a lightsource uniformly over the surface of the liquid crystal display panel10. There are several kinds of back light units 20 such as a direct backlight type (or direct type) and an edge light type.

Referring to FIG. 2, it is a cross-sectional view along line 2-2 of FIG.1 and depicts a back light module 21 of the direct type. The direct typeback light module 21 includes a housing 70 which has a reflective sheet60 disposed on the bottom surface of the housing 70, a lamp 50, such asa fluorescence cathode tube, disposed at the bottom portion of thehousing 70, a diffusing sheet 40 disposed on the upper surface of thehousing 70 and a prism sheet 30 disposed on the diffusing sheet 40.

Referring to FIG. 3, it is a cross-sectional view along line 2-2 of FIG.1 and depicts a back light module 22 of the edge light type. The edgelight type back light module 22 includes a light guide 80, a lamp 50which is attached to at least one edge of the light guide 80, and aU-shaped reflector 61 which surrounds the lamp 50. An open portion ofthe reflector 61 is disposed at the edge of the light guide 80, areflecting sheet 60 is disposed at the bottom of the light guide 80, adiffusing sheet 40 is disposed on the light guide 80 and a prism sheet30 is disposed on the diffusing sheet 40. Because the lamp 50 isdisposed at the edge of the light guide 80, the thickness of the LCD canbe relatively decreased.

The light guide 80 includes a printed dot pattern or a V-shaped notchedpattern 82 on at least one surface for scattering the light in the lightguide 80 and illuminating the liquid crystal display panel 10. The lightguide 80 and the dot pattern or V-shaped notched pattern 82 thereon aretypically made of PMMA by the process of press or ejection molding. Thediffusing sheet 40 is disposed on the light guide 80 and typically madeof half-transparent PET or polycarbonate for further evenly diffusingthe light emitted from the light guide 80. The prism sheet 30 isdisposed on the diffusing sheet 40 for gathering the diffused light fromthe diffusing sheet 40 in the direction perpendicular thereto.

Since the liquid crystal display panel 10 has a polarizing sheet fortransmitting the light with one polarizing direction and absorbing thelight with the other polarizing direction, about 50% of the energy ofthe light is lost when the light passes the polarizing sheet. Therefore,a polarization recycle film 35 is typically disposed on the prism sheet30 for reflecting the light with the other polarizing direction, and thereflected light then is reflected by the optical element therebeneathand recycled after the polarizing direction thereof is changed, therebyincreasing the brightness of the liquid crystal display. However, theabove-mentioned polarization recycle film is available typically from3M™ Company of St. Paul Minn. under the trade name Dual BrightnessEnhancement Film (DBEF), which causes the liquid crystal display up to160-170% brighter, but is significantly expansive. Further, the cost ofthe liquid crystal display will increase more and more as the dimensionof the liquid crystal display increases in recent years.

Generally, the back light module of the liquid crystal display shall beconstructed to meet the requirements of increasing power efficiency andthe screen brightness, providing uniform brightness, lowering powerconsumption and cost, as well as decreasing the dimension. Prior artattempts have been made to meet the requirements and, for example, canbe seen in U.S. Pat. No. 6,164,790 issued to Lee on Dec. 26, 2000, U.S.Pat. No. 5,477,422 issued to Hooker et al. on Dec. 19, 1995, and U.S.Pat. No. 5,485,354 issued to Ciupke et al. on Jan. 16, 1996. Thesepatents are all incorporated herein by reference.

Japan Patent Application No. 11 (1999)-233919, which is incorporatedherein by reference, discloses a fluorescent lamp with reflective filmfor a back light module of a liquid crystal display so as to avoid theinter-reaction between the adjacent lamps and further avoid thedecrement of illumination due to the inter-reaction.

Furthermore, U.S. Pat. No. 6,122,103 issued to Perkins on Sep. 19, 2000entitled “Broadband Wire Grid Polarizer For The Visible Spectrum”, whichis incorporated herein by reference, discloses a polarizer with metalgrid wires, which provides high transmittance and reflectance for theentire visible spectrum.

U.S. patent application Ser. No. 10/227,841 entitled “Panel Light SourceDevice And Back Light Module For Liquid Crystal Display Device”, filedon Aug. 27, 2002 and commonly assigned to the assignee of the presentapplication, discloses a back light module with metal grid wires and isincorporated herein by reference.

The conventional metal grid wire polarizer 90 substantially comprises atransparent substrate 92 made of glass and metal grid wires 94 disposedthereon, as shown in FIG. 4. Now referring to FIG. 5, it depicts thegraphic plot of transmittance Tp, Ts and the reflectance Rp, Rs of theP-polarization (polarizing direction perpendicular to the metal gridwires 94) and S-polarization (polarizing direction parallel to the metalgrid wires 94) of the metal grid wires 94 versus the ratio Ω of thewidth W to the pitch P of the metal grid wires 94, where the thickness Tof the metal grid wires 94 is about 0.1 μm and the wavelength of theincident light is about 0.545 μm (green light). Although the metal gridwires are easy to manufacture in the range of the ratio Ω from 0.5 to0.6, the transmittance Tp of the P-polarization (polarizing directionperpendicular to the metal grid wires) of the metal grid wires 94 iscomparatively low, as shown in the drawing.

Accordingly, there exists a need for a light source and/or a back lightmodule of a liquid crystal display capable of meeting theabove-mentioned requirements.

SUMMARY OF THE INVENTION

It is an object of the present invention to provide a polarized lightsource for providing the liquid crystal display with the polarized lightso as to increase the energy efficiency of the liquid crystal display.

It is another object of the present invention to provide a back lightmodule for providing the liquid crystal display with the polarized lightso as to increase the energy efficiency of the liquid crystal display.

In order to achieve the above objects, the present invention provides apolarized light source device comprising a light source, a reflector, atransparent substrate, an antireflection layer, and a plurality of metalgrid wires. The reflector surrounds the light source for reflecting thelight, and has an opening for emitting the light. The transparentsubstrate is disposed at the opening. The antireflection layer isdisposed on the transparent substrate. The metal grid wires are disposedon the antireflection layer for transmitting the light with apredetermined polarization therethrough.

The present invention further provides a polarized light sourcecomprising an illuminant, a reflective film, and a plurality of metalgrid wires. The reflective film surrounds the illuminant and has anopening for emitting the light. The metal grid wires are disposed at theopening for transmitting the light with a predetermined polarizationtherethrough.

The polarized light source according to the present invention can beattached to a liquid crystal display for illuminating a liquid crystaldisplay panel of the liquid crystal display.

Accordingly, the back light module or the polarized light sourceaccording to the present invention includes a polarizing element andthus provides the polarized light without lowering the energyefficiency. Also, the polarized light may be transmitted through thepolarizing film of the liquid crystal display to minimize the lightabsorbed by the polarizing film. Therefore, the back light module or thepanel light source according to the present invention dispenses with theexpensive optical film and still meets the requirements of increasingthe entire power efficiency, increasing the brightness, and lowering thecost of the liquid crystal display.

BRIEF DESCRIPTION OF THE DRAWINGS

Other objects, advantages, and novel features of the invention willbecome more apparent from the following detailed description when takenin conjunction with the accompanying drawing.

FIG. 1 is a perspective exploded schematic view of a liquid crystaldisplay according to the prior art.

FIG. 2 is a cross sectional schematic view along line 2-2 of FIG. 1 of adirect type back light module according to the prior art.

FIG. 3 is a cross sectional schematic view along line 2-2 of FIG. 1 ofan edge light type back light module according to the prior art.

FIG. 4 is a cross sectional schematic view of a conventional metal gridwire polarizer.

FIG. 5 is a graphical plot showing the relationship between the ratio Ωof the width to the pitch of the metal grid wires shown in FIG. 4, andthe transmittance and the reflectance thereof.

FIG. 6 is a cross sectional schematic view of a polarized light sourcedevice according to an embodiment of the present invention.

FIG. 7 is a cross sectional schematic view of a polarized light sourcedevice according to another embodiment of the present invention.

FIG. 8 is a partial enlarged cross sectional schematic view of apolarizer of the polarized light source device shown in FIG. 6.

FIG. 9 is a graphical plot showing the relationship between the ratio Ωof the width to the pitch of the metal grid wires shown in FIG. 6, andthe transmittance and the reflectance thereof.

FIG. 10 is a cross sectional schematic view of a liquid crystal displayusing the polarized light source device according to the presentinvention.

FIG. 11 is a cross sectional schematic view of another liquid crystaldisplay using the polarized light source device according to the presentinvention.

FIG. 12 is a cross sectional schematic view of a lamp according to anembodiment of the present invention.

FIG. 13 is a cross sectional schematic view of a lamp according toanother embodiment of the present invention.

FIG. 14 is a partial enlarged perspective schematic view of metal gridwires of the lamp shown in FIG. 12.

FIG. 15 is a cross sectional schematic view of a liquid crystal displayusing the lamp according to the present invention.

FIG. 16 is a cross sectional schematic view of another liquid crystaldisplay using the lamp according to the present invention.

DESCRIPTION OF THE EMBODIMENT

Referring to FIG. 6, it depicts a polarized light source device 100according to an embodiment of the present invention. The polarized lightsource device 100 comprises a light source, such as a lamp 150, areflector 161 surrounding the lamp 150, and a polarizer 192. The lamp150 can be a cold cathode fluorescent lamp (CCFL).

Now referring to FIG. 8, it depicts the polarizer 192 of the polarizedlight source device 100. The polarizer 192 comprises a transparentsubstrate 194, an antireflection layer 191 disposed on the transparentsubstrate 194, and metal grid wires 190 disposed on the antireflectionlayer 191. Light emitted from the lamp 150 is transmitted into thetransparent substrate 194, through the antireflection layer 191, and outof the metal grid wires 190. The transparent substrate 194 is made oftransparent material, such as glass and acrylic resin (PMMA), therefractive index of which is n_(s). The antireflection layer 191 is madeof transparent dielectric material, such as nitrogen silicide (Si-Nx),the refractive index of which is n_(m). The antireflection layer 191shown in the drawing is a single film coated on the transparentsubstrate 194, but it will be apparent to those skilled in the art thatthe antireflection layer 191 can be a multi-layer film coated on thetransparent substrate 194. The refractive index of the antireflectionlayer 191 is in the range between the refractive index n_(s) of thetransparent substrate 194 and the equivalent refractive index n_(a) ofthe metal grid wires 190, i.e. n_(s)>n_(m)>n_(a). Preferably, therefractive index n_(m) of the antireflection layer 191 is derived fromthe following equation:n _(m)≈√(n _(a) ×n _(s))

The thickness d of the antireflection layer 191 is derived from thefollowing equation:d≈¼×λ/n _(m)

-   -   where λ is the wavelength of the incident light.

In fact, the transparent substrate 194 is made of glass or PMMA, andthus the antireflection layer 191 should be made of the material ofwhich the refractive index is above about 1.5.

The metal grid wires 190 are parallel to the lamp 150, and spaced outand formed on the antireflection layer 191 such that the light with thepolarizing direction perpendicular to the metal grid wires 190(P-polarization), i.e. perpendicular to the longitudinal direction ofthe lamp 150, is transmitted and the light with the polarizing directionparallel to the metal grid wires 190 (S-polarization) is reflected.

According to the present invention, the metal grid wires 190 are made ofaluminum (Al), silver (Ag), copper (Cu) or alloy, and preferably aremade of aluminum. Preferably, the pitch P of the metal grid wires 190 isbelow about 300 nm, the thickness T of the metal grid wires 190 is inthe range from about 30 nm to about 200 nm, and the ratio of the width Wto the pitch P of the metal grid wires 190 is in the range from about0.1 to about 0.8.

Now referring to FIG. 9, it depicts the graphic plot of transmittanceTp, Ts and the reflectance Rp, Rs of the P-polarization (polarizingdirection perpendicular to the metal grid wires 190) and S-polarization(polarizing direction parallel to the metal grid wires 190) of thepolarizer 192 versus the ratio Ω of the width W to the pitch P of themetal grid wires 190. The transparent substrate 194 is made of glass,the thickness T of the metal grid wires 190 is about 0.1 μm, thewavelength of the incident light is about 0.545 μm (green light), andthe antireflection layer 191 is made of nitrogen silicide (Si-Nx) andthe thickness d of the antireflection layer 191 is 70 nm. As shown inthe drawings, the transmittance Tp of the P-polarization (polarizingdirection perpendicular to the metal grid wires 194) of the metal gridwires 190 is raised because of the existence of the antireflection layer191 when the ratio Ω is in the range from 0.5 to 0.6.

Now referring to FIG. 7, it depicts a polarized light source device 100′according to another embodiment of the present invention. The polarizedlight source device 100′ is similar to the polarized light source device100 and comprises a lamp 150′, a reflector 161′ surrounding the lamp150′, and a polarizer 192′. The polarizer 192′ has metal grid wires190′. The metal grid wires 190′ are perpendicular to the lamp 150′, andspaced out and formed on the antireflection layer 191′ such that thelight with the polarizing direction perpendicular to the metal gridwires 190′ (P-polarization), i.e. parallel to the longitudinal directionof the lamp 150, is transmitted and the light with the polarizingdirection parallel to the metal grid wires 190′ (S-polarization) isreflected.

Referring to FIG. 10, it depicts a liquid crystal display 200 using thepolarized light source device 100 according to the present invention.The liquid crystal display 200 comprises a liquid crystal display panel210 and a back light module 220. The liquid crystal display panel 210comprises two transparent substrates 212, 214 and liquid crystalmaterial 216 disposed therebetween. The outer surfaces of transparentsubstrates 212, 214 of the liquid crystal display panel 210 are coveredwith polarizing sheets 218, 219, and the inner surfaces thereof areprovided with switching elements for changing the alignments of themolecular of the liquid crystal material 216 and thus generating images.

The back light module 220 is of an edge light type and is served as apanel light device for evenly illuminating the liquid crystal displaypanel 210. The back light module 220 comprises the polarized lightsource device 100 according to the present invention, a wedge lightguide 280 and a plurality of layers of optical films, such as diffusingsheet 240 and a prism sheet 230. The diffusing sheet 240 is used forfurther evenly diffusing the light. The prism sheet 230 is commerciallyavailable from 3M™ Company of St. Paul Minn. under the trade nameBrightness Enhancement Film II (BEF II) for gathering the light in thedirection perpendicular thereto.

The light emitted from the polarized light source device 100 istransmitted into the light guide 280 via an incoming surface 284 of thelight guide 280. The light guide 280 is provided with scatteringelements 182, such as a printed dot pattern or a V-shaped notchedpattern on the bottom surface of the light guide 280, for scattering thelight in the light guides 180 and transmitting the light out of theupper surface or the outgoing surface 285 of the light guide 280 so asto serve as a uniform panel light source. The light guide 280 istypically made of PMMA by the process of press or ejection molding. Thelight guide 280 further comprises reflectors 260, 265 disposed in thebottom surface and the distal end of the light guide 280 for reflectingthe light back to the light guide 280.

Obviously, it will be apparent to those skilled in the art that thepolarizing direction of the polarizing sheet 219 on the liquid crystaldisplay panel 210 is corresponding to that of the polarized light sourcedevice 100 such that the brightness of the liquid crystal display 200 isincreased. Generally speaking, because of the arrangement of the liquidcrystal display, the back light module 220 according to the presentinvention is particularly adapted to be used with a thin film transistor(TFT) liquid crystal display panel of In-Plane-Switching, VerticalAlignment, and Multi-Domain Vertical Alignment.

Referring to FIG. 11, it depicts a liquid crystal display 300 using thepolarized light source device 100 according to the present invention.The liquid crystal display 300 is generally similar to the liquidcrystal display 200, wherein the similar elements are designated withthe similar reference numerals. The liquid crystal display 300 comprisesa liquid crystal display panel 110 and a back light module 320. The backlight module 320 is of the direct back light type and is provided with aplurality of polarized light source device 100 disposed in a housing370.

Accordingly, the back light module or the polarized light sourceaccording to the present invention provides the polarized light. Thepolarized light may be transmitted through the polarizing film of theliquid crystal display to minimize the light absorbed by the polarizingfilm. Therefore, the back light module or the panel light sourceaccording to the present invention dispenses with the expensive opticalfilm and still meets the requirements of increasing the entire powerefficiency, increasing the brightness, and lowering the cost of theliquid crystal display.

Now referring to FIG. 12, it depicts a polarized light source or lamp550 according to an embodiment of the present invention. The lamp 550 isapplied to a liquid crystal display, typically is a cold cathodefluorescent lamp (CCFL), and has an elongated tube structure. The lamp550 has a transparent substrate, such as a glass tube 552, a reflectivefilm 554 coated on the inside surface of the glass tube 552, mercuryvapor 558 filling the glass tube 552, and fluorescent material 556disposed between the mercury vapor 558 and the glass tube 552. Whilevoltage is applied to the both ends of the lamp 550, the mercury vapor558 can be excited such that the fluorescent material 556 emits visiblelight. The light emitted from the fluorescent material 556 is reflectedby the reflective film 554, and emits from an opening 553 of thereflective film 554. As shown in the drawing, the radial angle θ of theopening 553 is below 90 degree, and preferable in the range from about30 degree to about 90 degree.

The lamp 550 further comprises a plurality of metal grid wires 590,which are disposed at the opening 553 of the reflective film 554 and areparallel to the longitudinal direction of the lamp 550. Furtherreferring to FIG. 14, the metal grid wires 590 are spaced out and formedon the inside surface of the glass tube 552 such that the light with thepolarizing direction perpendicular to the metal grid wires 590 istransmitted and the light with the polarizing direction parallel to themetal grid wires 590 is reflected.

It will be apparent to those skilled in the art that the polarized lightsource device is not limited to the cold cathode fluorescent lamp(CCFL). Other light source device, such as an incandescent lamp such asa halogen lamp and a discharge lamp such as a xenon lamp and a neonlamp, can be provided with metal grid wires and a reflective film so asto serve as a polarized light source device. The polarized light sourcedevice according to the present invention has an illuminant, such as afilament in an incandescent and xenon in a xenon lamp, a reflective filmhaving an opening for projecting light, and a metal grid wire polarizerdisposed at the opening for generating polarized light.

Now referring to FIG. 13, it depicts a polarized light source or lamp550′ according to further another embodiment of the present invention.The lamp 550′ comprises a reflective film 554′ coated on the outsidesurface of the glass tube 552′ and having an opening 553′. A pluralityof metal grid wires 590′ are disposed on the outside surface of theglass tube 552′ at the opening 553′. The function of the metal gridwires 590′, which is similar to that of metal grid wires 590, is usedfor transmitting the light with the polarizing direction perpendicularto the metal grid wires 590′ and reflecting the light with thepolarizing direction parallel to the metal grid wires 590′.

Now referring to FIG. 14, it depicts metal grid wires 590 of the lamp550 according to an embodiment of the present invention. According tothe present invention, the metal grid wires 590 are made of aluminum,silver, copper or alloy, and preferably are made of aluminum.Preferably, the pitch P of the metal grid wires 590 is below about 300nm, the thickness T of the metal grid wires 190 is in the range fromabout 30 nm to about 200 nm, and the ratio of the width W to the pitch Pof the metal grid wires 590 is in the range from about 0.1 to about 0.8.The metal grid wires 590 according to the present invention and thereflective film 554 can be formed on the glass tube 552 by the sameprocess at the same time. Alternatively, the metal grid wires 590 can beformed by the additional process. It will be apparent to those skilledin the art that the orientation of the metal grid wires 590 can bevaried as desired.

Referring to FIG. 15, it depicts a liquid crystal display 500 using thelamp 550 according to the present invention. The liquid crystal display500 comprises a liquid crystal display panel 510 and a back light module520. The liquid crystal display panel 510 comprises two transparentsubstrates 512, 514 and liquid crystal material 516 disposedtherebetween. The outer surfaces of transparent substrates 512, 514 ofthe liquid crystal display panel 510 are covered with polarizing sheet518, 519, and the inner surfaces thereof are provided with switchingelements for changing the alignments of the molecular of the liquidcrystal material 516 and thus generating images.

The back light module 520 is served as a panel light device for evenlyilluminating the liquid crystal display panel 510. The back light module520 comprises the above-mentioned lamp 550, a U-shaped reflector 561surrounding the lamp 550, a wedge light guide 280 and a plurality oflayers of optical films, such as diffusing sheet 540 and a prism sheet530. The diffusing sheet 540 is used for further evenly diffusing thelight. The prism sheet 530 is commercially available from 3M™ Company ofSt. Paul Minn. under the trade name Brightness Enhancement Film II (BEFII) for gathering the light in the direction perpendicular thereto.

The light emitted from the lamp 550 which has a polarized directionperpendicular to the longitudinal direction of the lamp 550(perpendicular to the metal grid wires 590) is transmitted into anincoming surface 584 of the light guide 580. The light guide 580 isprovided with scattering elements 582, such as a printed dot pattern ora V-shaped notched pattern on the bottom surface of the light guide 580,for scattering the light in the light guides 580 and transmitting thelight out of the upper surface or the outgoing surface 585 of the lightguide 580 so as to serve as a uniform panel light source and illuminatethe liquid crystal display panel 510. The light guide 580 is typicallymade of PMMA by the process of press or ejection molding. The lightguide 580 further comprises reflectors 560, 565 disposed in the bottomsurface and the distal end of the light guide 280 for reflecting thelight back to the light guide 580.

Furthermore, in the light guide 580, the polarizing light is scatteredby the scattering elements 182 and transmitted into the liquid crystaldisplay panel 510. The polarization of the light which is transmittedinto the liquid crystal display panel 510 is substantially perpendicularto the metal grid wires 590. Therefore, the light absorbed by thepolarizing sheet 519 of the liquid crystal display panel 510 isdecreased so the light efficiency of the liquid crystal display 500 isincreased.

It will be apparent to those skilled in the art that the polarizingdirection of the polarizing sheet 519 on the liquid crystal displaypanel 510 is corresponding to that of the metal grid wires 590 such thatthe brightness of the liquid crystal display 500 is increased. Generallyspeaking, because of the arrangement of the liquid crystal display, theback light module 520 according to the present invention is particularlyadapted to be used with a thin film transistor (TFT) liquid crystaldisplay panel of In-Plane-Switching, Vertical Alignment, andMulti-Domain Vertical Alignment.

Now referring to FIG. 16, it depicts a liquid crystal display 600 usingthe lamp 550 according to the embodiment of the present invention. Theliquid crystal display 600 is generally similar to the liquid crystaldisplay 500, wherein the similar elements are designated with thesimilar reference numerals. The liquid crystal display 600 comprises aback light guide 620 of the direct type, which has a plurality of lamps550 disposed in a housing 670. The polarized light emitted from the lamp550 can be transmitted through the polarizing sheet 619 of the liquidcrystal display panel 610 and into the liquid crystal display panel 610.The polarized light can be transmitted through the polarizing sheet 619of the liquid crystal display panel 610 so that the light absorbed bythe polarizing sheet 619 is decreased and thus the light efficiency ofthe liquid crystal display 600 is increased.

Although the invention has been explained in relation to its preferredembodiment, it is not used to limit the invention. It is to beunderstood that many other possible modifications and variations can bemade by those skilled in the art without departing from the spirit andscope of the invention as hereinafter claimed.

1. A back light module for illuminating a liquid crystal display panelof a liquid crystal display, comprising: a polarized light source devicecomprising: a light source for generating light; a reflector surroundingthe light source for reflecting the light and having an opening foremitting the light; a transparent substrate disposed at the opening; anantireflection layer disposed on the transparent substrate; and aplurality of metal grid wires disposed on the antireflection layer fortransmitting the light with a predetermined polarization therethrough;and a light guide having at least one incoming surface facing thepolarized light source, a plurality of scattering elements, and anoutgoing surface, wherein the light emitted from the polarized lightsource is transmitted into the light guide from the incoming surface,scattered by the scattering elements, and then transmitted out of thelight guide from the outgoing surface.
 2. The back light module asclaimed in claim 1, further comprising: a plurality of optical filmsdisposed between the outgoing surface of the light guide and the liquidcrystal display panel.
 3. The back light module as claimed in claim 2,wherein the optical films comprise: at least one diffusing sheet fordiffusing the light emitted from the light guide; and at least one prismsheet for gathering the light in the direction perpendicular thereto. 4.The back light module as claimed in claim 1, wherein the metal gridwires are made of aluminum.
 5. The back light module as claimed in claim1, wherein the metal grid wires are made of a material selected from thegroup consisting of aluminum, silver, copper and alloys and combinationsthereof.
 6. The back light module as claimed in claim 1, wherein thepitch of the metal grid wires is below about 300 nm.
 7. The back lightmodule as claimed in claim 1, wherein the metal grid wires have athickness in the range from about 30 nm to about 200 nm.
 8. The backlight module as claimed in claim 1, wherein the ratio of the width tothe pitch of the metal grid wires is in the range from about 0.1 toabout 0.8.
 9. The back light module as claimed in claim 1, wherein theratio of the width to the pitch of the metal grid wires is in the rangefrom about 0.5 to about 0.6.
 10. The back light module as claimed inclaim 1, wherein the antireflection layer is made of a material, therefractive index of which is above about 1.5.
 11. The back light moduleas claimed in claim 1, wherein the antireflection layer is made ofnitrogen silicide (Si-Nx).
 12. The back light module as claimed in claim1, wherein the antireflection layer is a multi-layer film.
 13. The backlight module as claimed in claim 1, wherein the refractive index of theantireflection layer is in the range between the refractive index of thetransparent substrate and the equivalent refractive index of the metalgrid wires.
 14. The back light module as claimed in claim 1, wherein therefractive index n_(m) of the antireflection layer is derived from thefollowing equation:n _(m)≈√{square root over ((n _(a) ×n _(s)))} where n_(s) is therefractive index of the transparent substrate and n_(a) is theequivalent refractive index of the metal grid wires.
 15. The back lightmodule as claimed in claim 1, wherein the thickness d of theantireflection layer is derived from the following equation:d≈¼×λ/n _(m) where n_(m) is the refractive index of the antireflectionlayer and λ is the wavelength of the light emitted from the lightsource.